Famous Scotland Volcano Has Only One 'Heart'

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The land of the rings brings hundreds of pilgrims to a windswept
corner of western Scotland every year.

A journey around Ardnamurchan volcano's well-worn trails is an
annual rite of passage for geology students in Europe. Regular
tourists also brave the remote trek to the national geopark,
which protects 1 billion years of Earth's history.

Ardnamurchan's fame comes from an 83-year-old study that launched
volcano
science in Europe. The study, a meticulous geologic map of
ringlike structures preserved in the Ardnamurchan volcanic rocks,
revealed the volcano's hidden source: a series of three magma
chambers.

Now, it's time to rewrite history, scientists say.

Instead of three magma pulses, just one big push birthed
Ardnamurchan volcano, according to a study published Oct. 8 in
the journal Scientific Reports.

"What we see is one big magma
chamber. There's not three distinct places," said Steffi
Burchardt, lead study author and a geoscientist at the University
of Uppsala in Sweden. "It is much more like we see magma chambers
today."

Ardnamurchan is one of four extinct volcanoes on Scotland's
northwest coast that mark the opening of the North Atlantic Ocean
starting 60 million years ago. As Greenland drifted away, the
first floods of magma arrived from a
hotspot that now sits under Iceland. In epochs since,
glaciers ground away the tops of the volcanoes, leaving their
hearts exposed.

Nearly a century ago, British geologists mapped hundreds of thin,
cone-shaped intrusions at Ardnamurchan. The intrusions are magma
that pushed into underground cracks and cooled beneath the
surface. They're like guiding arrows, arranged in a ring,
narrowing down toward their source. [ The
10 Biggest Volcanic Eruptions in History ]

The original mappers, James Richey and Herbert Thomas, concluded
that three distinct magma chambers fed Ardnamurchan volcano,
because the "cone sheets," as the intrusions are called,
converged at three different spots.

But when Burchardt and her colleagues brought Ardnamurchan's
geologic map into the modern age, inputting the precisely mapped
structures into a 3D computer model, they encountered a surprise.

Instead of three meeting sites, the cone sheets focused on a
single, saucer-shaped chamber where the roiling molten rock once
awaited its release. The chamber lies about 1.5 kilometers (1
mile) below the current surface and was up to 6 km (4 miles) long
when active.

The size and alignment of the magma chamber created by the
computer model matches with recent geophysical surveys of the
volcano, as
well as displacements in sedimentary rocks, Burchardt said. (The
covering rocks were shoved and deformed as the magma pushed its
way upward.)

Burchardt said that since the 1930 study, knowledge of how
volcanoes form has advanced tremendously. "They were among the
scientists who laid the foundation of modern volcanology," she
said. "I guess if they had all the knowledge we had today, they
may have seen Ardnamurchan differently."

"The mountain is a real icon, so people have a bit of respect for
it," Burchardt told LiveScience's OurAmazingPlanet. "Maybe this
is the reason why scientists haven't dared touch it for a long
time."